Direct observation of active material interactions in flowable electrodes using X-ray tomography

Abstract

Understanding electrical percolation and charging mechanisms in electrochemically active biphasic flowable electrodes is critical for enabling scalable deionization (desalination) and energy storage. Flowable electrodes are dynamic material systems which store charge (remove ions) and have the ability to flow. This flow process can induce structural changes in the underlying material arrangement and result in transient and non-uniform material properties. Carbon-based suspensions are opaque, multi-phase, and three dimensional, and thus prior characterization of the structural properties has been limited to indirect methods (electrochemical and rheology). Herein, a range of mixed electronic and ionically conducting suspensions are evaluated to determine their static structure, function, and properties, utilizing synchrotron radiation X-ray tomographic microscopy (SRXTM). The high brilliance of the synchrotron light enables deconvolution of the liquid and solid phases. Reconstruction of the solid phase reveals agglomeration cluster volumes between 10 μm and 10μm (1 pL) for low loaded samples (5 wt% carbon). The largest agglomeration cluster in the low loaded sample (5 wt%) occupied only 3% of the reconstructed volume whereas samples loaded with 10 wt% activated carbon demonstrated electrically connected clusters that occupied 22% of the imaged region. The highly loaded samples (20 wt%) demonstrated clusters of the order of a microliter, which accounted for 63-85% of the imaged region. These results demonstrate a capability for discerning the structural properties of biphasic systems utilizing SRXTM techniques, and show that discontinuity in the carbon particle networks induces decreased material utilization in low-loaded flowable electrodes.

Unraveling charge transport in carbon flow-electrodes: Performance prediction for desalination applications

“…The value of this resistor, which we will term as "charge percolation resistance R cp " from here onwards, decreases with increasing conductivity of the flow-electrode. An increasing activated carbon content, for example, leads to an increased size of charge percolation networks [32] and an overall improved conductivity, which agrees with the discussion by Hatzell et al [5].…”

“…[14] Many different physical and chemical processes influence the performance of flowelectrodes in these processes, whose interactions are not fully understood yet. An increasing number of studies are investigating these interactions by means of modelling, [30,31] imaging methods [32] and electrochemical characterization methods. [6,11,31,[33][34][35][36] However, the influencing parameters and material characteristics on the performance as flow-electrode for specific applications still need further investigation.…”

Interphases in Electroactive Suspension Systems: Where Chemistry Meets Mesoscale Physics

“…The contribution of interface between current collector and slurry towards electrical resistance is shown to be both significant and insignificant . Two schools of thought explain the mechanism of electrical conductivity in slurries; one wherein particle networks are known to dominate and another wherein electron tunneling dominates such that distribution and size of particle clusters is more important . The zeta potential of conductive carbon suspensions in organic electrolyte also cannot be generalized to either always positive or always negative; furthermore, the size of the cation used in the electrolyte is shown to be significant .…”

Membrane-electrode assemblies for flow-electrode capacitive deionization

“…Earlier work always looked at charge transport from the conductive surface via the slurry electrode to the membrane as displayed in Figure 1a. [23,24,25] Contrary, when using the proposed MEAs, only the surface facing the membrane is conductive.…”